1. Field of the Invention
Exemplary embodiments of the present invention relate to light emitting diodes including compound semiconductors and to light emitting diodes suitable for AC operation.
2. Discussion of the Background
Light emitting diodes (LEDs) can be made of compound semiconductors including, for example, Group III nitride-based compound semiconductors which have been used in a wide range of applications including display devices and backlight units and also as light sources for general lighting as a replacement to existing incandescent lamps and fluorescent lamps.
Generally, an LED is repeatedly turned on/off depending on the direction of electric current applied by an AC power source. Thus, when the LED is directly connected to the AC power source, the LED does not continuously emit light and is liable to be damaged by the reverse current. To solve such problems of the LED, International Publication No. WO 2004/023568 (A1), entitled “Light-emitting device having light-emitting elements” by Sakai et. al proposes an LED that is directly connected to a high voltage AC power source.
FIG. 1 illustrates a conventional AC light emitting diode 1. Referring to FIG. 1, the AC light emitting diode 1 includes a plurality of rectangular light emitting cells 4, which are formed on an insulation substrate 2. Further, bonding pads 3a, 3b are formed on the substrate 2.
The conventional light emitting diode 1 includes an n-type electrode pad 6 and a p-type electrode pad 8 on each of the light emitting cells 4. The light emitting cell 4 is partially removed to a predetermined depth to expose part of a middle layer in the light emitting cell 4. The exposed layer is typically an n-type semiconductor layer, and the n-type electrode pad 6 is formed on a region of the exposed n-type semiconductor layer. The p-type electrode pad 8 is formed on a p-side region at the top of the light emitting cell 4. The bonding pads 3a, 3b and the light emitting cells 4 between the bonding pads 3a, 3b are connected to one another in series by wires 5. The p-type electrode pad 8 and the n-type electrode pad 6 of adjacent light emitting cells are connected to each other by the wire 5.
In such a conventional light emitting diode 1, if the distance between the n-type electrode pad 6 and the p-type electrode pad 8 is large in a corresponding light emitting cell 4, electric current is concentrated mostly near the p-type electrode pad 8 so that light is strongly emitted near the p-type electrode pad 8. Further, when p-type electrode pad 8 is located near the n-type electrode pad 6, brightness increases in a region between the p-type electrode pad 8 and the n-type electrode pad 6, but significantly decreases in a region between the p-type electrode pad 8 and a boundary of the light emitting cell 4. This results in significant deterioration in luminous uniformity of the light emitting diode and becomes a major hindrance in manufacture of large scale light emitting diodes.
In other types of conventional light emitting diodes, an n-type electrode pad and a p-type electrode pad may be diagonally disposed to face each other at opposite corners of a light emitting cell. However, in these types of light emitting diodes, brightness is high only near the p-type electrode pad 8, thereby causing non-uniform light emitting.